Object Serialization

Serializing objects - objects in sessions

serialize() returns a string containing a
byte-stream representation of any value that can be stored in
PHP. unserialize() can use this string to
recreate the original variable values. Using serialize to
save an object will save all variables in an object. The
methods in an object will not be saved, only the name of
the class.

In order to be able to unserialize() an object, the
class of that object needs to be defined. That is, if you have an object
of class A and serialize this, you'll
get a string that refers to class A and contains all values of variables
contained in it. If you want to be able to unserialize
this in another file, an object of class A, the
definition of class A must be present in that file first.
This can be done for example by storing the class definition of class A
in an include file and including this file or making use of the
spl_autoload_register() function.

// this is needed for the unserialize to work properly.include("classa.inc");

$s = file_get_contents('store');$a = unserialize($s);

// now use the function show_one() of the $a object. $a->show_one();?>

If an application is using sessions and uses
session_register() to register objects, these objects
are serialized automatically at the end of each PHP page, and are
unserialized automatically on each of the following pages. This means that
these objects can show up on any of the application's pages once they become
part of the session. However, the session_register() is
removed since PHP 5.4.0.

It is strongly recommended that if an application serializes objects, for use
later in the application, that the application includes the class definition
for that object throughout the application. Not doing so might result in an
object being unserialized without a class definition, which will result in
PHP giving the object a class of __PHP_Incomplete_Class_Name,
which has no methods and would render the object useless.

So if in the example above $a became part of a session
by running session_register("a"), you should include the
file classa.inc on all of your pages, not only page1.php
and page2.php.

Beyond the above advice, note that you can also hook into the serialization
and unserialization events on an object using the
__sleep() and
__wakeup() methods. Using
__sleep() also allows you to only
serialize a subset of the object's properties.

User Contributed Notes 2 notes

Reading this page you'd be left with the impression that a class's `serialize` and `unserialize` methods are unrelated to the `serialize` and `unserialize` core functions; that only `__sleep` and `__unsleep` allow you to customize an object's serialization interface. But look at http://php.net/manual/en/class.serializable.php and you'll see that there is a more straightforward way to control how a user-defined object is serialized and unserialized.